BOB DYLAN will be 50 on May 24, and alongside the celebratory avalanche of books comes Columbia's rich assemblage of recordings, the stuff of so many rumours and pirate editions in the last two decades. The 58 tracks rehabilitated here range across the whole of Dylan's career, from 'Hard Days in New York Town ', recorded in a Minnesota hotel room in 1961, right up to 'Series of Dreams', an out-take from the Oh Mercy album released in 1989. There are demo discs from the early 1960s, such as the piano version of 'Times they are a Changin'', prototypes of songs that were to emerge in very different guises - a truncated first run-through of 'Like a Rolling Stone' wedged into a 3/4 waltz rhythm, a stunning electric thrash through 'When the Night comes falling from the Sky' - as well as songs that he'd left to others to record, most notably 'Farewell Angelina', made famous by Joan Baez and appearing here complete with an extra surreal verse, and 'If not for You', given to George Harrison.

Not everything on the set is of such interest or such a standard - there is for instance, a laboured account with The Band of 'I shall be released' that has more nostalgic than musical value - but why Dylan should have chosen to suppress some of the tracks here is utterly baffling. 'Blind Willie McTell', recorded with Mark Knopfler during the Infidels sessions in 1983, is unquestionably one of his greatest songs, a profound tribute to the urban blues tradition from which he had learnt so much, yet it has never appeared officially before, and there are at least another dozen, a standard album's worth, that are out of the top drawer too.

If by definition this set is tangential to Dylan's development, and the milestone LPs - Highway 61 Revisited, Blonde on Blonde, Blood on the Tracks, Oh Mercy - will continue to chart the authorised account of his musical pilgrimage, this first volume of the Bootleg Series (with a second promised of the live concert recordings) offers a fresh slant on an extraordinary achievement, and a musician capable of constant renewal. And it refutes convincingly the notion that Dylan is a great songwriter but a lousy singer - the best of the performances, angry, trenchant, inspired, stamp the songs indelibly and definitively. If the hopelessly erratic stage appearances, incoherent interviews and alarmingly variable new albums have tarnished the image sometimes, it is thrilling to have Dylan's uniqueness confirmed again. The recordings come with a superb set of notes from John Bauldie, which represents rock scholarship at its most valuable and least pretentious.

Even if she has never managed to renew herself quite as vividly as Dylan, Joni Mitchell has survived more than 20 years with her distinct sensibility intact. I suspect every Joni Mitchell fan cherishes the hope that she will yet produce another album to match the best of her confessional, acoustic days, something to set alongside Blue or The Hissing of Summer Lawns. But in recent years she's tried to steer a course through the borderlands between folk, jazz and funk; in 1988 she produced the thoughtful Chalk Mark in a Rain Storm, and repeats much of the same mixture in Night Ride Home.

Yet the vocal lines still snake and slide as elegantly as ever, the harmonic progression have their own logic, and if the result sometimes seems too immaculately manicured, the lyrics can still be stiletto sharp. Mitchell's setting of Yeats' 'The Second Coming' is puzzling, but at least shows off the baroque loops of her vocal lines, while 'Come in from the Cold' reveals a 40-something casting a beady eye on the idealisms of her youth - 'We really thought we had a purpose, We were so anxious to achieve' - and 'Cherokee Louise' is a dark little tale of child abuse. Despite the laid-back riffs, the album goes out on a note of quiet introspection, definitely looking back rather than forward, anxiously rather than with optimism.

Roger McGuinn may not have released an album for more than a decade, but the first 12-string guitar chords of Back from Rio make the connection:almost every track has the sound that McGuinn stamped upon The Byrds in the late 1960s, and which has been much imitated since. With the help of the likes of Tom Petty and Elvis Costello, the new songs are invariably polished, but do nothing to extend McGuinn's range. Only one number threatens to break the mould:Costello's own 'You Bowed Down' is a characteristically acid piece of recrimination which McGuinn sings splendidly, yet without ever suggesting that he is totally involved.

REM's Out of Time on the other hand moves into genuinely new territory for a band that already could do little wrong on the college circuit, and made contact with a much wider audience with its last album, Green. There is a pared-down feeling to many of the numbers, with more directness in the lyrics as well as is in the presentation. Edges are smoother, the arrangements often lusher, and there are conscious echoes of the 1960s, including a topical piece of brooding Doors-iana and even some touches of surfin' harmonies. Everything about REM is impressive; while the point of some of the songs remains as obscure as ever, the sure shape of each number and the adroitness of the melodies are consistently effective.

And so finally to Green on Red's unavoidably enjoyable Scapegoats. This two-man outfit learnt a lot from Dylan and The Band, and is even more obliged to Neil Young, yet comes up with a brand of folk-rock that never takes itself too seriously, and deals with just the things every self-respecting red-neck rock band cherishes most - the heat and the dust, the relationships that turn sour. With the volume turned up it makes a mixture that's hard to resist.